#include <iostream>
#include <cmath>
using namespace std;
int main()
{
double m,R;
cin >> m >> R;
cout << 2*R*sin(M_PI/m)*m;
return 0;
}
I2luY2x1ZGUgPGlvc3RyZWFtPgojaW5jbHVkZSA8Y21hdGg+CnVzaW5nIG5hbWVzcGFjZSBzdGQ7CiAKaW50IG1haW4oKQp7IAoJZG91YmxlIG0sUjsKCWNpbiA+PiBtID4+IFI7Cgljb3V0IDw8IDIqUipzaW4oTV9QSS9tKSptOwpyZXR1cm4gMDsKfQ==